Geared transmissions typically function to change the rotational speed of a prime mover output shaft and an input shaft of a desired work output. In a vehicle, the prime mover may include a diesel or gasoline internal combustion engine. It should be noted that there are many more applications than automobiles and trucks. Locomotives are equipped with transmissions between their engines and their wheels. Bicycles and motorcycles also include a transmission. Speed-increasing transmissions allow large, slow-moving blades of a windmill to generate power much closer to a desired AC frequency. Other industrial applications exist. In each case, the motor and transmission act together to provide power at a desired speed and torque to do useful work. Geared transmissions have also been used in combination with electric motors acting as the prime mover.
Multiple speed transmissions have been coupled to high torque prime movers that typically operate within a narrow speed range, most notably structured as large displacement diesel engines of tractor trailers. Electric motors have a much wider speed range in which they operate effectively. However, the motor operates most efficiently at a single speed. Known multiple speed transmissions attempt to maintain an optimum operating speed and torque of the prime mover output shaft, but only approximate this condition due to the discrete gear ratios provided. Accordingly, a need for a simplified variable speed ratio power transmission device exists.
Many existing transmissions incorporate planetary gearsets within the torque path. A traditional planetary gear drive has three major components: a sun gear, an annulus ring gear and a planet carrier. When one of those components is connected to the prime mover, another is used as the output and the third component is not allowed to rotate. The input and output may rotate at different speeds, and may also rotate in opposite directions, with the ratio of input to output speeds being a fixed value. When the previously fixed third component is connected to a second input and forced to rotate, the transmission will have a continuously varying speed ratio dependent on the speeds of both the prime mover and this new second input. One example of such a planetary gear drive is made by Toyota. While planetary gearsets have been successfully used in vehicle power transmissions in the past, a need exists for a planetary drive and control system for optimizing the gear drive's efficiency and power density.